Preheat the oven to 350°F and grease a large ramekin (see note) with butter or cooking spray.
In a medium bowl, mix together the oil and sugar with a fork to combine. Add the egg white, vanilla, white vinegar, and food coloring. Mix to combine.
In a small separate bowl, combine the cocoa powder, flour, baking soda, and salt
Add half of the flour mixture to the wet ingredients and stir to combine. Add the buttermilk and stir to combine then stir in the rest of the flour mixture.
Pour the batter into the greased ramekin. Bake for 24-28 minutes until the cake is set on top, a toothpick comes out with just moist crumbs, and if you gently press the top of the cake it slightly bounces back.
While the cake cools, make the frosting. Stir together the butter, cream cheese, and vanilla with a fork in a small bowl - it doesn’t need to be completely combined. Mix in the powdered sugar until combined, thick, and creamy.
Either pipe on the frosting or spoon it on top of the cooled cake and enjoy!
